In the manufacturing process of a semiconductor substrate and the like, a cleaning step for removing particles deposited on the substrate therefrom has been hitherto essential. A single wafer type cleaning apparatus for executing the cleaning step uses the technique of cleaning a substrate by jetting out fine droplets of a cleaning liquid such as deionized water toward the substrate.
In such a cleaning apparatus, a two-fluid nozzle for producing droplets by mixing a cleaning liquid and a pressurized gas together to jet out a fluid mixture of the droplets and a gas toward the substrate has been widely used, as disclosed, for example, in Japanese Patent Application Laid-Open No. 2007-227878. Foreign materials such as particles deposited on the substrate are physically removed by the kinetic energy of the droplets of the cleaning liquid. Also, Japanese Patent Application Laid-Open No. 2000-533 discloses a cleaning apparatus that causes a piezoelectric element to expand and contract repeatedly at a frequency of an ultrasonic band, thereby emitting a mist of a cleaning liquid accelerated in one direction from a discharge port toward a substrate at a high speed.
As a technique for discharging droplets, on the other hand, Japanese Patent No. 3659593 discloses a droplet spraying apparatus that vibrates a thin film formed with discharge ports of an inverted tapered shape to produce droplets. Also, Japanese Utility Model Publication No. 7-7164 (1995) discloses a nozzle head for an inkjet printer in which a pipe of an annular shape formed with a notch is filled with ink, and in which a vibrator is attached to an outer peripheral wall surface of the pipe except where the notch is formed to vibrate the ink, whereby droplets of ink are emitted.